In many fields there is a need for positioning of objects with great accuracy. This is most important, for example in a scanning probe microscope, SPM, in which a sample and a probe must be moved towards each other before starting a scanning. A technique of carrying out such moving involves an inertia-type motor, according to the above description, in which excitation of a piezoelectric tube causes an extension of the same and a corresponding movement of an object connected therewith, whereupon the piezoelectric tube is very rapidly retracted as the excitation ceases, and owing to moment of inertia in the system, the object that is to be moved then stays in the position where it was located when the piezoelectric tube was in its excited position. A device of the above type is described in, for example, K. Svensson, F. Althoff and H. Olin, “A compact inertial slider STM”, Meas. Sci. Techn., 8, 1360-1362 (1997). This publication describes a device for micropositioning in a scanning tunnel microscope, comprising both a sample and a sharp scanning tip. The position of the sharp scanning tip relative to the sample is controlled by means of two concentric piezoelectric tubes, the inner tube being used for scanning of the sharp scanning tip and the outer tube being used for inertia movement of the sample. The construction also comprises a positioning unit including two parts, a first part, which is fixedly connected to the outer tube, and a second part, which holds the sample. The second part is slidingly arranged on the first part, the sliding surface being located in a plane which is not perpendicular to the sharp scanning tip. When applying, for example, a serrated waveshape to the piezoelectric element, displacements between these two parts occur as the acceleration exceeds the limit of the static friction between the parts. The two parts are arranged in such manner that, when sliding towards each other in said sliding surface, the sample arranged on the second part is moved so as to be closer or further away from the prod while at the same time the actual sample surface is continuously held perpendicular to the sharp scanning tip. This construction is very compact and has a number of desirable properties, such as a low noise level. However the construction is complicated and comprises two piezoelectric elements. A micropositioning device of a simpler design is therefore desirable, which has a short mechanical loop, to reduce the mechanical noise in the form of vibrations in the system. A simpler design of the system further contributes to reducing the risk that dirt and other external interference reduces or fully eliminates the function of the inertia-type motor. Furthermore the above prior-art construction is particularly adapted to scanning tunnel microscopy (STM), and a more general device for use in connection with e.g. scanning probe microscopy (SPM) and other applications is desirable.